There was some confusion when it was declared in "Encounter at Farpoint" that McCoy was "only" 137 years old. Granted, we didn't yet learn the year in which the episode took place, but when the season-ender suggested it was 2364 or 2363, the confusion grew: if McCoy was born in 2227 or 2226, he'd only be in his early forties in TOS, whereas DeForest Kelley was past his mid-forties. But the mismatch is not too pronounced.